3 “The effects of the eruption were felt worldwide“The effects of the eruption were felt worldwide. It ejected roughly 10 billion metric tonnes (10 cubic kilometres) of magma, and 20 million tons of SO2, bringing vast quantities of minerals and metals to the surface environment. It injected large amounts of aerosols into the stratosphere—more than any eruption since that of Krakatoa in Over the following months, the aerosols formed a global layer of sulfuric acid haze. Global temperatures dropped by about 0.5 °C (0.9 °F), and ozone depletion temporarily increased substantially.” -Wikipedia

4 Core Case Study: Studying a Volcano to Understand Climate ChangeA NASA scientist predicted that the 1991 Philippines explosion would cool the average temperature of the earth by 0.5Co over a 15 month period and then return to normal by 1995.His predictions were correct.Figure 20-1

6 Chapter Overview QuestionsHow have the earth’s temperature and climate changed in the past?How might the earth’s temperature and climate change in the future?What factors influence the earth’s average temperature?What are some possible beneficial and harmful effects of a warmer earth?

7 Chapter Overview Questions (cont’d)How can we slow projected increases in the earth’s temperature or adapt to such changes?How have human activities depleted ozone in the stratosphere, and why should we care?

8 PAST CLIMATE AND THE GREENHOUSE EFFECTOver the past 900,000 years, the troposphere has experienced prolonged periods of global cooling and global warming.For the past 1,000 years, temperatures have remained fairly stable but began to rise during the last century.

10 Average temperature over past 900,000 yearsAverage surface temperature (°C)Figure 20.2Science: estimated changes in the average global temperature of the atmosphere near the earth’s surface over different periods of time. Although a particular place might have much lower or much higher readings than the troposphere’s average temperature, such averages provide a valuable way to measure long-term trends. QUESTION: What two conclusions can you draw from these diagrams? (Data from Goddard Institute for Space Studies, Intergovernmental Panel on Climate Change, National Academy of Sciences, National Aeronautics and Space Agency, National Center for Atmospheric Research, National Oceanic and Atmospheric Administration)Thousands of years agoFig. 20-2a, p. 465

11 Temperature change over past 22,000 yearsAgriculture establishedTemperature change (C°)End oflast iceageAverage temperature over past10,000 years = 15°C (59°F)Figure 20.2Science: estimated changes in the average global temperature of the atmosphere near the earth’s surface over different periods of time. Although a particular place might have much lower or much higher readings than the troposphere’s average temperature, such averages provide a valuable way to measure long-term trends. QUESTION: What two conclusions can you draw from these diagrams? (Data from Goddard Institute for Space Studies, Intergovernmental Panel on Climate Change, National Academy of Sciences, National Aeronautics and Space Agency, National Center for Atmospheric Research, National Oceanic and Atmospheric Administration)Years agoFig. 20-2c, p. 465

12 Temperature change over past 1,000 yearsTemperature change (C°)Figure 20.2Science: estimated changes in the average global temperature of the atmosphere near the earth’s surface over different periods of time. Although a particular place might have much lower or much higher readings than the troposphere’s average temperature, such averages provide a valuable way to measure long-term trends. QUESTION: What two conclusions can you draw from these diagrams? (Data from Goddard Institute for Space Studies, Intergovernmental Panel on Climate Change, National Academy of Sciences, National Aeronautics and Space Agency, National Center for Atmospheric Research, National Oceanic and Atmospheric Administration)YearFig. 20-2d, p. 465

13 Average temperature over past 130 yearsAverage surface temperature (°C)Figure 20.2Science: estimated changes in the average global temperature of the atmosphere near the earth’s surface over different periods of time. Although a particular place might have much lower or much higher readings than the troposphere’s average temperature, such averages provide a valuable way to measure long-term trends. QUESTION: What two conclusions can you draw from these diagrams? (Data from Goddard Institute for Space Studies, Intergovernmental Panel on Climate Change, National Academy of Sciences, National Aeronautics and Space Agency, National Center for Atmospheric Research, National Oceanic and Atmospheric Administration)YearFig. 20-2b, p. 465

16 How Do We Know What Temperatures Were in the Past?Scientists analyze tiny air bubbles trapped in ice cores learn about past:troposphere composition.temperature trends.greenhouse gas concentrations.solar, snowfall, and forest fire activity.Figure 20-3

22 How Do We Know What Temperatures Were in the Past?In 2005, an ice core showed that CO2 levels in the troposphere are the highest they have been in 650,000 years.Figure 20-4

23 384 ppm in 2007 392 ppm in 2011 280 ppm in 1725 Figure 20.4Concentration of carbon dioxidein the atmosphere (ppm)Carbon dioxide280 ppm in 1725Variation of temperature (C°)from current levelFigure 20.4Science: atmospheric carbon dioxide levels and global temperature. Estimated long-term variations in average global temperature of the atmosphere near the earth’s surface are graphed along with average troposphere CO2 levels over the past 160,000 years. The rough correlation between CO2 levels in the troposphere and temperature shown in these estimates based on ice core data suggests a connection between the two variables. In 2005, an ice core showed that CO2 levels in the troposphere are the highest they have been in 650,000 years. QUESTION: What are the implications of these data on your lifestyle now and in the future? (Data from Intergovernmental Panel on Climate Change, National Center for Atmospheric Research, and Physics Institute at the University of Bern, Switzerland)Temperature changeEnd of last ice ageThousands of years before presentFig. 20-4, p. 466

24 The Natural Greenhouse EffectFour major factors shape the earth’s climate:The sun.Greenhouse effect warms the earth’s lower troposphere and surface because of the presence of greenhouse gases.Oceans store CO2 and heat, evaporate and receive water, move stored heat to other parts of the world.Natural cooling process through water vapor in the troposphere (heat rises).Evaporation cools the Earth’s surfaceCondensation in clouds releases heat in upper troposphere

25 Major Greenhouse GasesThe major greenhouse gases in the lower atmosphere are, IN ORDER:water vapor- most important greenhouse gascarbon dioxide- greatest effect from human activitiesmethane- CH4 -more powerful greenhouse gas per molecule than CO2, but less of it than CO2nitrous oxide- N2O -comes from fertilizers and planting rice

26 Major Greenhouse GasesThe major greenhouse gases in the lower atmosphere are:water vapor carbon dioxide methane nitrous oxide.These gases have always been present in the earth’s troposphere in varying concentrations.Fluctuations in these gases, plus changes in solar output and Earth’s Mankelovich cycles are the major factors causing the changes in tropospheric temperature over the past 400,000 years.

27 Major Greenhouse GasesIncreases in average concentrations of three greenhouse gases in the troposphere between 1860 and 2004, mostly due toFossil fuel burning (CO2 & CH4)Deforestation (CO2 & N2O)Agriculture (N2O)Figure 20-5

28 392 ppm in 2011 384 ppm in 2007 280 ppm in 1725 Fig. 20-5a, p. 467Figure 20.5Science: increases in average concentrations of three greenhouse gases—carbon dioxide, methane, and nitrous oxide—in the troposphere between 1860 and 2005, mostly because of fossil fuel burning, deforestation, and agriculture. The fluctuations in the CO2 curve (top) reflect seasonal changes in photosynthetic activity, which cause small differences between summer and winter concentrations of CO2. (Data from Intergovernmental Panel on Climate Change, National Center for Atmospheric Research, and World Resources Institute)Fig. 20-5a, p. 467

29 Figure 20.5Science: increases in average concentrations of three greenhouse gases—carbon dioxide, methane, and nitrous oxide—in the troposphere between 1860 and 2005, mostly because of fossil fuel burning, deforestation, and agriculture. The fluctuations in the CO2 curve (top) reflect seasonal changes in photosynthetic activity, which cause small differences between summer and winter concentrations of CO2. (Data from Intergovernmental Panel on Climate Change, National Center for Atmospheric Research, and World Resources Institute)Fig. 20-5b, p. 467

30 Figure 20.5Science: increases in average concentrations of three greenhouse gases—carbon dioxide, methane, and nitrous oxide—in the troposphere between 1860 and 2005, mostly because of fossil fuel burning, deforestation, and agriculture. The fluctuations in the CO2 curve (top) reflect seasonal changes in photosynthetic activity, which cause small differences between summer and winter concentrations of CO2. (Data from Intergovernmental Panel on Climate Change, National Center for Atmospheric Research, and World Resources Institute)Fig. 20-5c, p. 467

31 CLIMATE CHANGE AND HUMAN ACTIVITIESEvidence that the earth’s troposphere is warming:The 20th century was the hottest century in the past 1000 years.The 14 hottest years since 1861 have been since 1990

32 CLIMATE CHANGESince 1900, the earth’s average tropospheric temperature has risen 0.6 C°.Over the past 50 years, Arctic temperatures have risen almost twice as fast as those in the rest of the world.

33 CLIMATE CHANGEGlaciers and floating sea ice are melting and shrinking at increasing rates.The range of specific species is moving to higher altitudes (up mountains) and higher latitudes.What happenes to the size of a species’ habitat as it moves up a mountain?

34 Figure 19.5Melting of Alaska’s Muir Glacier in the popular Glacier Bay National Park and Preserve between 1948 and Mountain glaciers are now melting almost everywhere in the world. Question: How might melting glaciers in Alaska and other parts of the world affect your lifestyle?Fig. 19-5a, p. 501

35 Figure 19.5Melting of Alaska’s Muir Glacier in the popular Glacier Bay National Park and Preserve between 1948 and Mountain glaciers are now melting almost everywhere in the world. Question: How might melting glaciers in Alaska and other parts of the world affect your lifestyle?Fig. 19-5b, p. 501

36 Sept. 1979 Sept. 2007 Russia Russia North pole North pole GreenlandAlaska (U.S.)Alaska (U.S.)Figure 19.6The big melt. Each summer, some of the floating sea ice in the Arctic Sea melts. But in recent years, rising atmospheric and ocean temperatures have caused more and more ice to melt. Satellite data show a large drop in the average cover of summer arctic sea ice between 1979 and In 2007 alone, the sea ice shrank by an area equal to that of six Californias or two Alaskas, much more than in any year since 1979 when scientists began taking satellite measurements. Such summer ice may be gone by 2030, and perhaps by as early as 2013, according to an estimate made by NASA climate scientist Jay Zwally in Question: Do you think that the increased melting of floating arctic sea ice is part of a positive or negative feedback loop (p. 45)? Explain? (Data U.S. Goddard Space Flight Center, NASA, National Snow and Ice Data Center)CanadaCanadaFig. 19-6, p. 501

37 Effects on Biodiversity: Winners and LosersPossible effects of global warming on the geographic range of beech trees based on ecological evidence and computer models.Next

38 Beech Future range Overlap Present range Fig. 20-13, p. 478Figure 20.13Natural capital degradation: possible effects of global warming on the geographic range of beech trees based on ecological evidence and computer models. According to one projection, if CO2 emissions doubled between 1990 and 2050, beech trees (now common throughout the eastern United States) would survive only in a greatly reduced range in northern Maine and southeastern Canada. Similarly, native sugar maples would likely disappear in the northeastern United States. QUESTION: What difference does it make if the range of beech trees changes? (Data from Margaret B. Davis and Catherine Zabinski, University of Minnesota)OverlapPresentrangeFig , p. 478

39 CLIMATE CHANGE AND HUMAN ACTIVITIESWarmer temperatures in Alaska, Russia, and the Arctic are melting permafrost, releasing more CO2 and CH4 into the troposphere (feedback loop…which kind, positive or negative?)During the last century, the world’s sea level rose by cm, mostly due to runoff from melting of land-based ice and the expansion of ocean water as temperatures rise.

42 The Scientific Consensus about Future Climate ChangeThere is strong evidence that human activities will play an important role in changing the earth’s climate during this century.Coupled General Circulation Models (CGCMs) couple, or combine, the effects of the atmosphere and the oceans on climate.

43 Coupled General Circulation Model of the Earth’s ClimateSimplified model of major processes that interact to determine the average temperature and greenhouse gas content of the troposphere.Figure 20-6

45 Consensus projection is 5 °C ↑ by 2100 if we “do nothing”Measured and projected changes in the average temperature of the atmosphere (2005).↑ 0.6 °C since 1900Consensus projection is 5 °C ↑ by 2100 if we “do nothing”Consensus is 4 °C ↑ could threaten civilization as we know itFigure 20-7

46 Most recent data suggests that temperatures are increasing even faster than the worst-case 2007 IPCC estimatesFigure 20.7Natural capital degradation: comparison of measured changes in the average temperature of the atmosphere at the earth’s surface between 1875 and 2005 and the projected range of temperature increase during the rest of this century. QUESTION: If these projections are valid, list three ways this will affect your lifestyle. (Data from U.S. National Academy of Sciences, National Center for Atmospheric Research, and Intergovernmental Panel on Climate Change, Hadley Center for Climate Prediction and Research)Fig. 20-7, p. 470

47 Why Should We Be Concerned about a Warmer Earth?A rapid increase (non-linear response pattern) in the temperature of the troposphere during this century would give us little time to deal with its harmful effects.As a prevention strategy scientists urge to cut global CO2 emissions 50% over the next 50 years…. “50/50”This could prevent changes in the earth’s climate system that might last for tens of thousands of years (due to many positive feedback loops)

48 FACTORS AFFECTING THE EARTH’S TEMPERATURESome factors can amplify (positive feedback) and some can dampen (negative feedback) projected global warming.There is uncertainty about how much CO2 and heat the oceans can remove from the troposphere and how long the heat and CO2 might remain there.Warmer temperatures create more clouds that could warm or cool the troposphere.

49 Human Effects on the Carbon CycleBurning fossil fuels for energyResidentialCommercialIndustrialTransportationClearing forests for agriculture & forest productsCovering land with pavementExponential population growth

50 Effects of Higher CO2 Levels on PhotosynthesisIncreased CO2 in the troposphere can increase plant photosynthesis (PS) but:The increase in PS would slow as the plants reach maturity.Carbon stored by the plants would be returned to the atmosphere as CO2 when the plants die & decayIncreased PS decreases the amount of carbon stored in the soil.

51 FACTORS AFFECTING THE EARTH’S TEMPERATUREAerosol and soot pollutants produced by human activities can warm (SO4 aerosols) or cool (soot particulates) the atmosphere, but such effects will decrease with any decline in outdoor air pollution.Warmer air can release methane gas stored in bogs, wetlands, and melting tundra soils and accelerate global warming (feedback?).

52 EFFECTS OF GLOBAL WARMINGA warmer climate would have beneficial and harmful effects but poor nations in the tropics would suffer the most.Some of the world’s floating ice and land-based glaciers are slowly melting and are helping warm the troposphere by reflecting less sunlight (“albedo”) back into space (feedback?).

55 Rising Sea LevelsChanges in average sea level over the past 250,000 years based on data from ocean cores.Figure 20-9

56 Rising Sea LevelsIf sea levels rise by 9-88cm during this century, most of the Maldives islands and their coral reefs will be flooded.Figure 20-11

57 Warm, shallow current Cold, salty, deep current Fig. 20-12, p. 476Figure 20.12Natural capital: a connected loop of shallow and deep ocean currents stores CO2 in the deep sea and transports warm and cool water to various parts of the earth. This loop results when ocean water in the North Atlantic near Iceland is dense enough (because of its salt content and cold temperature) to sink to the ocean bottom, flow southward, and then move eastward to well up in the warmer Pacific. A shallower return current aided by winds then brings warmer and less salty—and thus less dense—water to the Atlantic. This water can cool and sink to begin the cycle again. A warmer planet would be a rainier one, which, coupled with melting glaciers, would increase the amount of freshwater flowing into the North Atlantic. This could slow or even jam this loop by diluting the saltwater and making it more buoyant (less dense) and less prone to sinking. Historical evidence suggests that such shifts in ocean currents have sometimes taken place in a matter of years or decades. QUESTION: How might your lifestyle be affected if this loop slows down in your lifetime?Cold, salty,deep currentFig , p. 476

58 Changing Ocean CurrentsIt has recently been shown that the potential shifting of ocean currents is less of a threat than we thought before.Global warming could alter ocean currents and cause both excessive warming and severe cooling.Next

59 EFFECTS OF GLOBAL WARMINGOceans remove 25-30% of tropospheric CO2A warmer troposphere can decrease the ability of the ocean to remove and store CO2 bydecreasing the nutrient supply for calcareous phytoplankton that store CO2 in their calcium carbonate (CaCO3) shells, by potentially disrupting wind and ocean currents that provide nutrients via upwelling (feedback?)

60 EFFECTS OF GLOBAL WARMINGIncreasing the acidity of ocean water:CO2 is dissolved in the ocean as carbonic acid, H2CO3increased acidity interferes with calcareous phytoplankton shell formationIncreased acidity dissolves existing deposits of CaCO3 (feedback?)CO2 is less soluble in warmer water (feedback?)

61 EFFECTS OF GLOBAL WARMINGGlobal warming will lead to prolonged heat waves and droughts in some areas (Africa, Asia, & Western USA) and prolonged heavy rains and increased flooding in other areas (Europe; more intense hurricanes and typhoons).Between 1979 & 2002, the area of Earth’s land experiencing severe drought increased between 15% and 30%

62 EFFECTS OF GLOBAL WARMINGIn a warmer world, agricultural productivity may increase in some areas (Canada & Russia) and decrease in others (Asia & Africa)….why?Crop and fish production in some areas could be reduced by rising sea levels that would flood river deltas (why?).Global warming will increase deaths from:Heat and disruption of food supply.Spread of tropical diseases to temperate regions.Increase the number of environmental refugees.

63 DEALING WITH GLOBAL WARMINGClimate change is such a difficult problem to deal with because:The problem is global.The effects will last a long time.The problem is a long-term political issue.The harmful and beneficial impacts of climate change are not spread evenly.Many actions that might reduce the threat are controversial because they can impact economies and lifestyles.

64 DEALING WITH GLOBAL WARMINGTwo ways to deal with global warming:Mitigation that reduces greenhouse gas emissions.Adaptation, where we recognize that some warming is unavoidable and devise strategies to reduce its harmful effects.

65 Adaptation StrategiesDevelop crops thatneed less waterWaste less waterConnect wildlifereserves with corridorsMove people awayfrom low-lyingcoastal areasStockpile 1- to 5-yearsupply of key foodsMove hazardous materialstorage tanks awayfrom coastProhibit new constructionon low-lying coastal areasor build houses on stiltsFigure 20.17Solutions: ways to prepare for the possible long-term effects of climate change. QUESTIONS: Which three of these adaptation solutions do you think are the most important?Expand existingwildlife reservestoward poles(why?)Fig , p. 485

67 Solutions: Reducing the ThreatWe canimprove energy efficiencyrely more on carbon-free renewable energy resourcesfind ways to keep much of the CO2 we produce out of the troposphere (Carbon Capture & Sequestration a.k.a. CCS)

68 Removing and Storing CO2Methods for removing CO2 from the atmosphere or from smokestacks and storing (sequestering) it.Figure 20-15

69 down from rig for deep ocean disposal Abandoned oil field Crop field Spent oil reservoir isused for Crop fieldTanker deliversCO2 from plantto rigCoalpowerplantOil rigTree plantationCO2 is pumpeddown from rig for deep ocean disposalAbandonedoil fieldCrop fieldSwitchgrassCO2 deposit CO2 is pumped down to reservoir through abandoned oil fieldFigure 20.15Solutions: methods for removing carbon dioxide from the atmosphere or from smokestacks and storing (sequestering) it in plants, soil, deep underground reservoirs, and the deep ocean. QUESTION: Which two of these mitigation solutions do you think are the most important?Spent oil reservoir isused for CO2 deposit= CO2 pumping= CO2 depositFig , p. 482

70 Problems with CCS Unproven technologyPromotes continued use of fossil fuelsRequires huge government subsidies that draw funds from other solutionsThere can be no leaks for any reason

72 DEALING WITH GLOBAL WARMINGA crash program to slow and adapt to climate change now is very likely to cost less than waiting and having to deal with its harmful effects later.As usual, “An ounce of prevention is worth a pound of cure”

73 WHAT IS BEING DONE TO REDUCE GREENHOUSE GAS EMISSIONS?Getting countries to agree on reducing their greenhouse emissions is difficult.But…A 2006 poll showed that 83% of Americans want more leadership from federal government on dealing with global warming.

74 International Climate Negotiations: The Kyoto Protocol (1997)Treaty on global warming which first phase went into effect January, 2005 with 189 countries participating.It requires 38 participating developed countries to cut their emissions of CO2, CH4, and N2O to 5.2% below their 1990 levels by 2012.Developing countries were excluded.The U.S. and Australia did not sign, but California (world’s 6th largest economy) and Maine are participating.U.S. did not sign because developing countries such as China, India and Brazil were excluded.

75 Moving Beyond the Kyoto ProtocolCountries could work together to develop a new international approach to slowing global warming (much has changed since 1997)The Kyoto Protocol will have little effect on future global warming without support and action by the U.S., China, and India.November 29- December 9, 2011: Durban, South Africa Climate Change ConferenceSee Forbes article

76 Actions by Some Countries, States, and BusinessesIn 2005, the EU proposed a plan to reduce CO2 levels by 1/3rd by 2020.Global companies (BP, IBM, Toyota) have established targets to reduce their greenhouse emissions to 10-65% below 1990 levels by 2010.

77 Actions by Some Countries, States, and BusinessesCalifornia has adopted a goal of reducing its greenhouse gas emission to 1990 levels by 2020, and 80% below by 2050.The US EPA refused California’s request to set tough new standards(!)

78 Actions by Some Countries, States, and BusinessesBP spent $20 million to lower it’s greenhouse gas emissions to 10% below 1990 levels.Took 3 years, from 1998 to 2001Saved $250 million

79 • Drive a fuel-efficient car, walk, bike, carpool, What Can You Do?Reducing CO2 Emissions• Drive a fuel-efficient car, walk, bike, carpool,and use mass transit• Use energy-efficient windows• Use energy-efficient appliances and lights• Heavily insulate your house and seal all drafts• Reduce garbage by recycling and reuse (why?)• Insulate your hot water heater• Use compact fluorescent bulbs• Plant trees to shade your house during summerFigure 20.16Individuals matter: ways to reduce your annual emissions of CO2. QUESTION: Which three of these actions do you think are the most important? What ones do you do?• Set water heater no higher than 49°C (120°F)• Wash laundry in warm or cold water• Use low-flow shower head• Buy products from companies that are trying to reduce their impact on climate• Demand that the government make climatechange an urgent priorityFig , p. 485

80 OZONE DEPLETION IN THE STRATOSPHEREDuring four months of each year up to half of the ozone in the stratosphere over Antarctica and a smaller amount over the Arctic is depleted.Figure 20-19

81 OZONE DEPLETION IN THE STRATOSPHERELess ozone in the stratosphere allows for more harmful UV radiation to reach the earth’s surface.The ozone layer keeps about 95% of the sun’s harmful UV radiation from reaching the earth’s surface.Chlorofluorocarbons (CFCs) have lowered the average concentrations of ozone in the stratosphere.In 1988 CFCs were no longer manufactured, due to the Montreal Protocol

83 OZONE DEPLETION IN THE STRATOSPHERESince 1976, in Antarctica, ozone levels have markedly decreased during October and November.Figure 20-20

84 OZONE DEPLETION IN THE STRATOSPHEREOzone thinning: caused by CFCs and other ozone depleting chemicals (ODCs).Increased UV radiation reaching the earth’s surface from ozone depletion in the stratosphere is harmful to human health, crops, forests, animals, and materials such as plastic and paints.

85 • Immune system suppressionNatural Capital DegradationEffects of Ozone DepletionHuman Health• Worse sunburn• More eye cataracts• More skin cancers• Immune system suppressionFood and Forests• Reduced yields for some crops• Reduced seafood supplies from reduced phytoplankton• Decreased forest productivity for UV-sensitive tree speciesWildlife• Increased eye cataracts in some species• Decreased population of aquatic species sensitive to UV radiation• Reduced population of surface phytoplanktonFigure 20.21Natural capital degradation: expected effects of decreased levels of ozone in the stratosphere. QUESTION: Which five of these effects do you think are the most important?• Disrupted aquatic food webs from reduced phytoplanktonAir Pollution and Materials• Increased acid deposition• Increased photochemical smog• Degradation of outdoor paints and plasticsFig , p. 488Global Warming• Accelerated warming because of decreased ocean uptake of CO2 from atmosphere by phytoplankton and CFCs acting as greenhouse gases

86 Squamous Cell CarcinomaThis long-wavelength(low-energy) form of UV radiation causes aging of the skin, tanning, and sometimes sunburn. It penetrates deeply and may contribute to skin cancer.This shorter-wavelength (high-energy) formof UV radiation causes sunburn, prematureaging, and wrinkling. It is largely responsiblefor basal and squamous cell carcinomasand plays a role in malignant melanoma.UltravioletAUltravioletBThin layer ofdead cellsHairSquamous cellsEpidermisBasal layerSweatglandMelanocyte cellsDermisBasal cellBloodvesselsFigure 20.22Science: structure of the human skin and the relationships between ultraviolet (UV-A and UV-B) radiation and the three types of skin cancer. (Data and photos from the Skin Cancer Foundation)Squamous Cell CarcinomaBasal Cell CarcinomaMelanomaFig , p. 489

88 Reducing Exposure to UV RadiationWhat Can You Do?Reducing Exposure to UV Radiation• Stay out of the sun, especially between 10 A.M. and 3 P.M.• Do not use tanning parlors or sunlamps.• When in the sun, wear protective clothing and sun–glasses that protect against UV-A and UV-B radiation.• Be aware that overcast skies do not protect you.• Do not expose yourself to the sun if you are takingantibiotics or birth control pills.Figure 20.23Individuals matter: ways to reduce your exposure to harmful UV radiation. QUESTION: Which three of these actions do you think are the most important? Which ones do you do?• Use a sunscreen with a protection factor of 15 or 30anytime you are in the sun if you have light skin.• Examine your skin and scalp at least once a month formoles or warts that change in size, shape, or color orsores that keep oozing, bleeding, and crusting over. Ifyou observe any of these signs, consult a doctorimmediately.Fig , p. 490